In the manufacture of electrical coils, it has been common practice to provide metal terminals in the flanges of the coil bobbins. The operator attaches the wire to one terminal, winds the required number of turns, and then ties the wire to the other terminal and severs it. But when a tap is required, the operator must stop winding, draw a loop, and attach it to another terminal before resuming winding.
By way of example, winding may be done on a semi-automatic machine of the kind comprising a rotating arbor on which the bobbin is mounted, and a traversing wire guide which feeds the wire under controlled tension to the bobbin. The winder may have a controller which has programmed into it the number of turns per layer and the number of layers in the winding. To make a coil, the operator twists the end of the wire around the appropriate terminal on the bobbin and pushes the start button. Typically the machine winds the first layer at low speed before switching to high speed; the controller stops the machine whenever a tap must be made. At such time, the operator pulls a length of wire from the guide to make a loop, directs it to the appropriate terminal location, and then restarts the machine. This is repeated for as many taps as are needed. Finally the machine stops at the end of the winding, the wire is attached to the last terminal and severed. The operator then removes the bobbin from the arbor, trims the excess wire from the terminals and solders the wire ends to the terminals by dipping into a solder bath. Alternatively contact terminals may be used which do not require soldering, but which are crimped to penetrate the insulating varnish on the wire and establish electrical contact.
Winding machines are also used in which the bobbin is mounted on a stationary arbor and the wire is supplied to a rotating winding head which wraps it around the bobbin. With these machines too, the same need is present of having to stop winding whenever a tap is required. The foregoing starting and stopping of the coil winding machine slows down production so that it is inefficient, and requires the continuous attention of an operator which makes it expensive.
The objects of the invention are to provide improved bobbins and electrical coil constructions along with methods of winding coils which greatly reduce the extent of operator intervention required during winding. In particular it is desired to eliminate the need to stop the machine and have the operator intervene to draw a loop and restart the machine for every tap in the winding.